Figure 2. Geometric mean ratios (95% CI) of community water system (CWS) arsenic concentrations per higher percent of adults with a high school diploma, based on spatial lag quadratic spline models with knots at the 10^th and 90^th percentiles of the socioeconomic vulnerability score distribution.

Lines represent the geometric mean and green shaded areas surrounding the lines represent 95% confidence intervals. Shaded gray bars represent the county-level distribution of socioeconomic status vulnerability scores and are shown as “% of Counties” in the right y-axis. Models adjust for the percentage of public water drawn from groundwater sources, population density, median household income, and county racial/ethnic composition (the proportion of residents who are non-Hispanic Black, American Indian/Native Alaskan, non-Hispanic Asian, non-Hispanic White, and Hispanic/Latino). The reference was set to the 5^th percentile of the distribution of the percent of adults with a high school diploma. Models considering spline knots at other percentiles (50^th, 75^th) yielded similar findings. Spatial neighbors were identified via a simple queen contiguity matrix for neighbors (i=1) versus non-neighbors (i=0).